Dental implants used to stabilize dentures or support dental crowns and bridges have been known and have been used fairly extensively in the recent past. Such prior art devices are typically comprised of three components, namely, an implant component for anchoring to the bone, a transgingival component and a separate support component. The support component usually attaches to the transgingival component which, in turn attaches to the anchoring component at about the level of the bone. An artificial tooth or bridge may then be attached to this separate support component. This support component is sometimes referred to as an abutment portion, the transgingival component is sometimes referred to as an abutment portion, the transgingival component is sometimes referred to as an abutment connection or the transgingival collar or the transepithelial connection and the implant is sometimes referred to as a fixture.
An example of such a prior device may be found in Canadian Patent No. 1,313,597. This patent describes as implant for insertion into bone through an epithelial and fibrous connective tissue layer to which a prosthesis may be attached. This implant comprises a top portion for supporting a mechanical component to which the prosthesis may be connected and a body comprising an upper bone attachment region which tapers to a lower bone engagement region having a porous surface. The upper bone attachment region comprises a substantially non-porous but bioreative surface and this patent teaches that this results in an upper bone attachment region which is claimed to be capable of enhancing bone attachment.
However, several problems develop with an implant of this type. In particular, the patent teaches use of a collar 14 that is adapted to be coupled to the implant 12. However the interface between the collar 14 and the implant 12 occurs at a level below the gingiva in the installed position. Further, although the patent teaches providing recesses 40 on the lower surface 42 of the collar 14 to compliment projections 32 of the implant 12 to prevent rotation between the two components, in practice this is not effective. The attachment between the collar and the implant is accomplished by means of a threaded screw identified as 46 in FIG. 1. Such a screw has a natural tendency to become loose during the vigorous stresses to which an implant of this type is subjected.
To avoid problems associated with the loosening of the threaded screw 46, practitioners have resorted to insertion of cement into the threaded portion to ensure a locked and non-loosening joint between the implant component and the support component. Unfortunately, because the interface between the collar and the implant is below the gum level, any excess cement will be squeezed out at the interface and may not be noticed by the practitioner since it is hidden from view. Such excess accumulation of cement can create irritation of the gum and the bone and can result in infection and/or implant failure.
In addition, all implant system, (fixture, abutment connection, abutment) which have this type of arrangement have a microgap between the fixture or implant and the abutment connection or the transgingival collar at the level of the bone. This microgap has been called an "endotoxin generator" by some authorities because it is a region for potential bacterial growth.
Other prior art devices include implants with threaded exteriors which require extensive and complicated methods for preparation of the gum and bone to accept the insert. As a result, such implants are difficult and expensive to insert and the surgery is most often done by specialists. In any event they are not practical and result in excess discomfort for the patient and unnecessary difficulties for the dentist making the installation. For example, some require incising the gym to gain access to the bone; multiple drilling and reaming steps; installation of the implant; reattachment, by suturing or the like, of the gum over the implant site to promote healing; a return visit several months later to the dental office to have the gum again incised to allow access to the implant; insertion and attachment of the abutment portion; and final attachment of the prosthesis to the abutment portion. The first incision into the gym can promote scaring, making the second incision difficult.